阿尔泰山山前活动断裂带内现今地应力状态及稳定性分析

新疆阿尔泰地区分布着亚洲大陆内部一个规模宏大的活动构造带,同时,历史地震资料也显示阿尔泰山是一个比较活跃的地震带,分析断裂带内现今地应力状态对评价其地震活动的危险性具有重要意义。通过对布置在阿尔泰山山前活动断裂带内2个近700 m的深孔进行原位水压致裂法地应力测试,揭示了活动带内现今应力状态分布规律。结果表明:测试范围内空间主应力状态在埋深320 m左右由逆断型向走滑型转换,进而说明该复合断层近场存在应力分区现象;两孔实测最大水平主应力方位主要呈NW向,与震源机制解综合印证了区内NWW向断裂右旋走滑的活动特征。最后,基于实测地应力资料,结合库伦摩擦滑动准则及Byerlee定律对研究区内活动断裂的稳定性进行了力学分析,分析得出截至目前该活动断裂尚未具备诱发失稳的力学条件,处于相对稳定状态。这为其现今活动性研究补充了新的基础地质力学资料,为近场有关工程项目的选址提供科学参考。

Current In-situ Stress State and Stability of Active Fault Zone in Piedmont of Altai Mountains

There is an active tectonic zone in large scale in Altai region of the Asian continent,and historical earth-quake data shows that the Altai Mountain is also active in seismicity. Analyzing the current stress state is of great significance to the assessment of earthquake activity risk. In this research, the distribution law of current in-situ stress state in the active fault zone is revealed by hydraulic fracturing measurement at two boreholes(nearly 700 m in depth) in the piedmont of Altai Mountains. Results show that in buried depth of about 320 m,the spatial princi-pal stress state changes from thrust type to strike-slip type,indicating a stress partition near the active faults;the o-rientation of maximum horizontal principal stress of the two boreholes is mostly in NW,which,together with the fo-cal mechanism,verifies the right-lateral strike-slip characteristics of NWW active faults. Finally, according to the measured stress data,mechanical analysis on the stability of the active faults is carried out based on Coulomb faul-ting criterion and the law of Byerlee.Results conclude that up until now,the active faults in the piedmont of the Al-tai Mountains are relatively stable,with no mechanical condition brewing instability. The research results offer basic geomechanics data for studies on the regional active faults' current activity,and provide scientific reference for se-lecting the location of engineering project near the active faults.